# CVE-2026-58100: FreeBSD kqueue out-of-bounds read in fork copy

Source: https://junglewise.ai/threats/cve-2026-58100-kqueue-fork-copy-knote-indexed-into-the-child-s-file-descriptor  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-15. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-58100 · Severity: info · Published 2026-10-15

FreeBSD's kqueue is a system mechanism for scalable event notification used by applications to handle many concurrent events efficiently. A memory safety bug in the copy-on-fork implementation could allow an unprivileged local attacker to read out-of-bounds memory and escalate privileges on affected systems.

Technologies: [Freebsd](https://junglewise.ai/threats/technologies/freebsd). Vendors: [Freebsd](https://junglewise.ai/threats/vendors/freebsd).

## Quick answers

**Is CVE-2026-58100 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-58100 being exploited in the wild.

**How severe is CVE-2026-58100?** Informational severity, published 15 October 2026.

**Which products and versions are affected?** Freebsd 15.1 (prior to 15.1-RELEASE-p4).

**Is there a fix for CVE-2026-58100?** Yes: fixed in FreeBSD 15.1-RELEASE-p4 and later; stable/15 after commit 5db05b5dedf3. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-58100 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-58100?** Check whether you run Freebsd at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in FreeBSD 15.1-RELEASE-p4 and later; stable/15 after commit 5db05b5dedf3

## Technical details

CVE-2026-58100 is an out-of-bounds read in kqueue_fork_copy_knote() where file descriptor numbers are used to index into the child's file descriptor table without bounds checking. Because the child's FD table is copied before knotes are transferred, a concurrent thread in the parent can grow the parent's table and register knotes with FD numbers beyond the child's table bounds, causing an out-of-bounds read. This is a race condition requiring local access.

## Affected products

- FreeBSD FreeBSD 15.1 (prior to 15.1-RELEASE-p4)

## Timeline

- 2026-09-29: disclosed: FreeBSD Security Advisory FreeBSD-SA-26:65.kqueue published
- 2026-09-29: patched: Corrections committed to stable/15 and releng/15.1

## References

- [https://security.freebsd.org/advisories/FreeBSD-SA-26:65.kqueue.asc](https://security.freebsd.org/advisories/FreeBSD-SA-26:65.kqueue.asc)

## Related threats

- [FreeBSD kernel kqueue memory safety bugs in copy-on-fork](https://junglewise.ai/threats/cve-2026-58099-when-copying-knotes-from-a-parent-kqueue-to-a-child-the-copy-code)
- [FreeBSD kernel heap out-of-bounds access in semop(2)](https://junglewise.ai/threats/cve-2026-58098-when-semop-2-blocks-waiting-for-a-semaphore-condition-it-releases)
- [FreeBSD sound(4) use-after-free in buffer resize TOCTOU race](https://junglewise.ai/threats/cve-2026-101308-when-an-audio-channel-s-buffer-needs-to-be-resized-the-sound-4)
- [FreeBSD RACK stack buffer overflow in tcp_rack](https://junglewise.ai/threats/cve-2026-101307-when-the-pcm-sample-array-needs-to-grow-the-rack-stack-doubles-a)
- [FreeBSD jail filesystem root escape via SCM_RIGHTS](https://junglewise.ai/threats/cve-2026-101306-scm-rights-file-descriptor-passing-did-not-preserve-fd-resolve)